Gear cutter



7 g F. HODGKINSON GEAR CUTTER 2 Sheets-Sheet 1 Filed Aug. 11 1920 INVENTOR.

' A TTORNEY 9ct. 7-, 1924. 1,511,077 F. HODGKINSON GEAR CUTTER Filed Augll 1920 2 Sheets-Sheet 2 BYV ATTORNEY Patented Cet. 7, 1924.

FRANCIS HODGKINSON. F SNARTHMORE PENNSYLVNIA. ASSIGNOR TO WESTING- HOUSE GEAR VANIA..

AND DYNAIYIOMETER COMPANY.

A CORPORATION OF PENNSYL- GEAR CUTTER.

Apnlicationv filed August 11, 1920. Serial No. 402.806`

T 0 all whom if #my Conner/i.'

Be it known that l., FnANCIs Hononivsox a subject of the Kino; ot Great, Britain and Ireland, and a resident of Swarthmore, in the county ot Delaware and State ot' Penn sylvania. have invented new and useful Improvement in Gear Cutters. ot' which the following' is a speciiication.

This invention reiates to `fear cut ing machines ot the type intended t'or the cutting of relatively lrggror high-power and high-speed gears especially7 ot the reduction type ordinarilyT employed tor speed reduc tion purposes in connection with steam turbines.

An object ot my invent ion =`o provide a driving;- mechanism for the table ot a gear cutting machine which includes plurality of pairs of meshing gear tooth elements so disposed that the points ot engagement ot the meshing tooth elements vary progressively thereby providing; Ytor the transini,suv sion of motion from the driving afenls to the frear table at a more uni't'orni rate than has been done heretofore.

Another object ot my invei'ition the provision ot a worm driven mechanism 'for a gear cutter in which a plurality ot driving Worms meshes .'itli a common driven worm and in which the driving worms are disposed relatively to the triven worin fear that progressive errors ot pitch and contour errors of teeth are compensated tor,

These and other objects are attained hy means of apparatus eailiodyinq the iefitu'e-L: herein described and illustrated in draw` ings accompanying;V and formingi a part oi this application.

In the drawings.4 Fien l is a trao'me'uary vicW of a gear cutting? machine shoviuq my invention applied thereto: Fifi "2 is a diagrammatic view showinfr another torn of my invention; and Fie: is a view of gear teeth for the purpose ot explainngj the invention.

In the construction ot hio'h-speed and high-power gearing such. tor instance, as is used for speed reduction in connection with turbines, it is desirable that the `rears be cut with as great a degree ol" accuracy as possible in order to insure the ctlicient transmission of power and the elimination or reduction of noise. ln other words the circular pitch should be unitorin and the contours of the teeth should be accurate. ln

practice, it has been found to be ditlicult to out gears. especially ot very large size, without introducing reproduction errors ot the transmission employed in the gear cutting machine. lt will be obvious that, it the rear train drivingV the `fear table has either or both errors in pitch or ot the contour ot' the teeth` such errors will be reproduced in the blank being hobbed. ccordine'ly`r it is the purpose ot my invention to provide a transmission for a fear cutting machine table which will minimize the reproduction of the errors oi transmission on the gear beingr cut.

li'iei'erringr to Fig. l. a gear table 9 is shown rotatable about a vertical axis and is supported by the carriage 10. The table is provided with a plurality ot superposed worm gears l2. i3. le1V and l5 which are designed to be driven by means of driving worms 16. 17. i8 and 19 carried` respectively. by the drivingsha'ttg Q0. 2l. 22 and At one end the carriace l() supports a standard 25 and the latter is provided with bearings tor snpi'iortinn the right hand ends or the shai'ts l0 2l. 22 and "lf3 Beyond the bearings of the bcarinol sipnort. the shafts have connected, respectively. thereto the bevel or mitre ne QT QS., :ufl f0, or 'the shafts mayv be driven in any desired man ner. The lother cn'ls ot' the a"ts ill 2'2 and 273 are supported in thrust bearinfrs Si 23 and 3i. respective-lv the lower thrist bear-:ntfs dl and 3Q beine; connecte-l to a whitiletre lever :in'l the uper Av"ris' bearings 32 afd 537i no c vrect-=l t whiii'lereo lever Bti The wo wliitlieree 'e vers f2.5 and 3G are ronnccted by means of links 3T and 38 to the wbitiictr'ci lever 39 whi'h is pivote/l ty the standard `l-"i carried by tb..n sunnortiwf carriage. lt will be seen that thc whiiiietre" construction a'nounts to a doubletree ai' atonement wherebyY pressure is eoualizfe'l between several drivin-v shafts.

The riitre or beel pinions QT. QQ. Q9 and S0 are driven respectively by bevel nears 41 46. 4T and 4R and the latter are supported by a vertical shaft 49 carried bv bearings in the standard Q5, The lower end ot the shaft 49 is provided with a bevel gear "il driven by a bevel Qear 51 journaled in and carried by a downwardly projecting! portion ot' the carria'e. the bevel `ear being splined to the shaft 7:2 whereby power is transmitted regardless ot' the position of on the side of the pivot 71 opposite the thrust bearing 69, is connected, by means of a link 76, to the other end of the hell crank lever of an adjoining lever mechanism. The structure then includes four driving worms mounted on shafts and each shaft has a thrust bearing associated therewith. Each of the thrust bearings is supported by means of a lever mechanism such as that ust described and the lever mechanisms are connected in series by means of the links 76 connecting the respective bell cranks 74 and the respective thrust bearing supporting levers 70. The shaft is driven by an appropriate driving means, such, for instance, as the gear 80 and the worm shafts 65, 66, 67 and 68 are inter-geared so that they all rotate together When power is applied to shaft 65. Any system of interconnecting gearing may be employed in order to secure the simultaneous and equal rate of rotation of these shafts. As shown in Fig. 2 the bevel gear 81 drives the bevel gear 82, the latter being connected to a shaft Y1`he shaft 83 is connected to shaft 86 by bevel gears 84 and 85, the shaft 86 driving the worm shaft 68 through the gears 87 and 88; the shaft 86 is connected to the shaft 91 by bevel gears 89 and 90, the latter shaft being connected to the worin shaft 67 by means of bevel gears 92 and 93; and the shaft 91 drives the Worm shaft 66 by means of a system of gearing employing bevel gears 94, 95, the shaft 96, and the bevel gears 97 and 98. lVhereas the means for driving and the means for supporting the Worms, as above set forth, are preferred by me, it will he obvious that any desired supliiorting and driving means might be employed so long as the essential characteristics of the pressure equalization and the progressive meshing of the worms. above set forth. are retained.

From the description of my invention as above set forth. the operation thereof will be obvious to those skilled in the art. It will be apparent that the same underlying fundamental principle exists in the two modifications. that is. applicant has a phirality of meshing gear tooth elements between a driving shaft and driven element and so arranged relatively that the points of engagement of the gear elements progressively vary one-quarter of the pitch distance. when referred to one of the driven gears, to the pitch of the driven elements.

lt will he seen that the combination of the Worms with the interconnected system of supporting levers and bearings results in the worm wheel being driven at a more uniform rate. 1n Fig. 2. an arrangement is shown whereby both errors in the circular pitch and errors in the contour of the teeth are compensated for. These desirable ref stilts are achieved by the use of a pressure equalization system for supporting die worms and by so disposing the worms relatively to the gear that corresponding points of meshing differ progressively by a Vtraction of the pitch determined by the number ot' worms employed. In the construction shown. as above set forth, four worms being employed. a corresponding point of meshing in each worin with the worm gear varies progressively and successively by one-quarter of the pitt-h; how ever, it will be obvious that the progresv sion needed might be successive but vai-jv in any mainer so long as the desired series of the corresponding points progressively varying in the manner set forth is retained.

It will be apparent that gears of still greater accuracy may be cut by utilizing the principles of my invention if the gears of the gear cutting machine are produced in the saine manner. In other words, if the machine employs gears in its drive cut in accordance with the principles of my invention, the errors of pitch and contour would be small, and if my system of compensation is employed therewith, the errors, if any, reproduced would be exceedingly minute.

lVliile l have shown my invention in but two forms, it will be obvious to those skilled in the art that it is not so limited` but is susceptible of various other changes and modifications without departing from the spirit thereof. and l desire. therefore. that only such limitations shall he placed ther-fupon as are imposed by the prior art or as are specifically set forth in the appended claims.

hat lY claim is:

1. In a gear-cutting machine. the combination of a plurality of pairs of meshing driving and driven worm elements. shafts for supporting the driving worm elements, lever mechanism for interconnecting the shafts to equalize pressure` and driving' mechanism for the other ends of the shafts, the points of engagement of said driving Worm elements being in advance of each other by a fraction of the pitch determined by the number of driving worin elements.

2. In a gear-cutting machine, the combination of a turn table, a plurality of pairs of meshing driving and driven worin elements for driving the turn table, shafts for supporting the driving worm elements, 1ever mechanism for interconnecting the shafts to equalize pressure, a thrust bearing between each shaft and the lever mechanism, and driving mechanism for the other ends of the shafts, the points of engagement of the driving Worms being in advance of each other by a fraction of the pitch determined by the number of the Worms.

3. In a gear-cutting machine. the combinati-on ot a turn table. a pluralitv ot' pairs ol' meshing gear elements for driving the 'urn table. drivin.; shai'tt carrviue ot the eiements. pressure equaliz' g tor the shafts. and a thrust hearingr between .f ch shaft and the pressure-equaiizing' means. the points of enga;i lent of the teeth of the driving gear elements being' in advance of each other bv c traction o? the Ditch determined bj? the number o? driving gear elements.

l. In a` geancuttine' uuchine. the wunbination of a driven eieiucut. a piuralit;- ot Worm gears carried thereby. a pluraitv ot .vorins'uieshing with the vvorm eje-ars and havingT the points ot ei\-;meinent ther With the worin gears in advance nt earn other b v a fraction ot the pitch detcrul led bv the number ot Worms, a driinej siiat tor each Worin. and pressi:re-equaliiug means for connecting` the shaft.

In a gear-cutting' machine. thicombination ot` a driven element, a pluralitv of Worin `gears carried therebv. a oluralitv ot drivingfr worms meshing' with the vvmjm fears and having points oli engl'agen'leut thereof with respect to the Worin gea rs iu advance of each other bv a traction ot' the pitch deter mined bv the number ot driving` Worms. a driving' shaft for each worin.. lever means for equalizingl the pressure between the shafts. and thrust bearings between shatts and the lever means.

G. In a gear cutting machine the combination ol a table, tour superposed Worin gears farried bv the table and relativelv spaced angularlv oneeauarter oi the pitch distance @t the gears, vvornis fesbine with the Worm gears. drivingshams tor the Worms. and pressure equalizinnj means tor supporting the drivingr shatts at a single end.

7. In a gear cutting machine. the combination of a' table, tour Worin gears rof equal pitch connected thereto, the teeth of the vvoriu gears being so arranged as to be in advancd one over the other. of onceuarter :1? *l pitch distance. a driving Worin for mh ci' the vform gears, a driving shaft connected to each Worin. lever mechanism tor interconnecting these shafts at a single end and thrust bearings between the shafts and lever mechanism.

In a gear cuttingr machine. the combination of a rotatable table. a movable carriage tor the table. a pluralityY of superuosed worm gears connected to the table. a driving Worm t'or each of the worin lgears, the points of engagement of the Worms with the Worin gears progressivelv varying by distances corresponding; to a fractional part ot' the pitch determined bv the nuniber of worms. pressure equalizing means for supporting` the shafts at one end. supporting means carried by the carriage for the equalizingmeans. and drivin@T means supported b v the carriage and connected to the shafts at the other end,

In a lgear cutting machine. the combination of a table. a movable carriage for supportinga the table. four Worm gears of equal pitch connected to the table and pro- KQressivelnv spaced one trom the other. substantially one-tourth of the pitch. driving .vorms meshing With the Worin gears, pressure ecuaiiziuir means for supporting the shafts at one end, thrust bearings arranged between each shaft and the pressure equalicing` means. a support tor the pressure equali/.ingr means connected to the carriage, and driving means tor the shafts at the other end carried bv the movable carriage.

In testimony whereof, I have hereunto subscribed my name.

FRANCIS HODGKVNSON. 

